There are existing automated meter reading (AMR) power line carrier (PLC) systems that provide for PLC communication between a data concentrator at a substation and a meter installed down the power line in the low voltage service territory. However, most current systems have shortcomings, including single point access, limited capacity, low data rates, additional equipment to bypass the distribution transformer and, above all, lack of scalability. Very low data rates are required in order to provide overall communication reliability, which translates directly into a scalability limitation. For example, prior art systems have utilized transmit and receive frequencies as low as in the audio range in order to pass through distribution transformers. Some of these frequencies are integral multiples of the line frequency (n×fline, where n does not exceed 100), and others are simple fractions of the line frequency (fline/(2n), where n>1). The prior art employing the latter technique allows an energy consumption signal to be superimposed on the power signal at a frequency lower than that of the power signal itself. This places a limitation on the data rates that the system can deliver. The limitation on scalability is primarily caused by the limited number of meters that can be communicated with at one time and the manual programming required when changes are made to the service territory. Overall, the shortcomings of current systems include lack of reliability, flexibility, and scalability.
PLC systems make it possible to analyze network disturbances using electrical connectivity. Using PLC systems, the supply of electricity can be much more directly verified, as compared to systems that depend on wireless coverage. Various prior art PLC have used polling mechanisms to detect outages, while others have kept the meter and data collector continuously in communication. Also, there are prior art systems that report an outage event by a battery-backed up system that senses loss of power and activates a modem that relays the power loss information. One disadvantage of such systems is that when many meters simultaneously lose power, the concurrent “last gasp” messages can create considerable collisions and noise.
SCADA-like systems use transceivers at substations and various infrastructure points (e.g., distribution transformers and substation feeders) to check the status of the power transmission network. These transceivers constantly monitor the operation of such instruments and relay information when a fault is encountered.
What are needed are AMR systems that require minimal manual intervention and are scalable as the number of installed meters increases, either due to mandatory procedures in place or due to high energy costs and the need to eliminate unmetered services. As utilities strive to reduce operating costs, a system that is economically scalable and overcomes some or all of the above-mentioned problems is highly desirable. The scalability issue also implies that an automated system that the utility can install across the entire service territory (including multiple generating stations) or a subsection thereof (including multiple substations), which provides a single-point control which provides data and status of installed meters, is needed. In addition, any technological progress that lowers the cost per metering point for a large system (e.g., more than 500 meters) by eliminating any additional equipment required at each transformer for PLC signaling is always welcomed by utilities.
It is a goal of this invention to present a two-way PLC AMR system that avoids the above-mentioned shortcomings of the prior art systems.
The current invention, in at least one embodiment, comprises a two-way communication system for reading interval metering data over medium tension distribution lines (4-33 kV), traversing distribution transformers to the metering devices on low tension lines (120-600 volts), without requiring any special equipment at the distribution transformers, while maintaining a reliable and cost effective AMR solution.
The use of power lines for signaling, meter reading, load control, and other communication purposes has been well documented (see, for example, U.S. Pat. No. 6,947,854, to Swarztrauber, incorporated herein by reference). In a network installation with a population of more than one meter, and a transponder accessing this population, the technology described by Swarztrauber presented a PLC communication system that included programming the meter to a specific channel (one of 16 in each of two bands that cover 15-35 kHz). The transponder could remotely program the channel of each meter by utilizing a “base channel” that all meters could recognize, to direct each meter to its proper “resting” channel, isolated from the other channels by a sufficient frequency difference to allow simultaneous communications of each transponder to each meter.
However, as the system size grows, following the above procedure, each transponder requires at least two unique frequencies to avoid interference from other installed devices using RF communication over power lines. In addition, the system maintains a cross reference list at the transponder, listing the meters for which the transponder is responsible. In an environment with multiple transponders and multiple polyphase devices, cross coupling of PLC signals can result in degradation of the overall throughput.